Philadelphia Air Quality in December
Across 2019–2025, Philadelphia's December air quality had a median AQI of 57 (Moderate) over 217 monitored days in the Philadelphia-Camden-Wilmington, PA-NJ-DE-MD area. 2.8% of December days (6 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 91.7% of days. The cleanest December on record here was 2024 (median AQI 52, 0 days above 100) and the worst was 2023 (median 61, 3 days above 100, peak AQI 108).
- Good: 24.4%
- Moderate: 72.8%
- Unhealthy for Sensitive Groups: 2.8%
- Unhealthy or worse: 0.0%
Reduce Indoor Ozone in Philadelphia
Today's main pollutant in Philadelphia is ground-level ozone (AQI 44). Important: standard HEPA filters do NOT remove ozone — only a purifier with a substantial activated-carbon bed adsorbs it. The biggest wins are cutting indoor sources (gas appliances, certain "ionizer" purifiers) and ventilating when outdoor ozone is low (early morning). A high-carbon unit helps with the gases and VOCs that linger indoors.
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How is the air in Philadelphia in December?
Moderate on a typical day: median AQI 57 across 2019–2025, with 2.8% of December days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓24.4% of December days were Good (AQI 0–50), 72.8% Moderate (51–100).
- ✓6 days of 217 reached AQI 101+; the December peak was 133.
- ✓Best December: 2024; worst December: 2023.
Frequently asked questions
What is the air quality like in Philadelphia in December?▾
Across 2019–2025, the median daily AQI in Philadelphia in December was 57 (Moderate). 24.4% of days were Good, 72.8% Moderate, and 2.8% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is December a good time for outdoor exercise in Philadelphia?▾
A typical December day in Philadelphia is Moderate (median AQI 57): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 36 of December days (2.8%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Philadelphia's December air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 91.7% of December days in Philadelphia. The highest December AQI recorded in 2019–2025 was 133 (Unhealthy for Sensitive Groups), in 2023.
Philadelphia December air quality, year by year
Philadelphia December air quality by year (Philadelphia-Camden-Wilmington, PA-NJ-DE-MD, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 31 | 59 | 2 | 133 | PM2.5 |
| 2020 | 31 | 56 | 0 | 87 | PM2.5 |
| 2021 | 31 | 63 | 0 | 84 | PM2.5 |
| 2022 | 31 | 57 | 1 | 113 | PM2.5 |
| 2023worst | 31 | 61 | 3 | 108 | PM2.5 |
| 2024cleanest | 31 | 52 | 0 | 85 | PM2.5 |
| 2025 | 31 | 54 | 0 | 86 | PM2.5 |
What December air means in Philadelphia
A typical December day in Philadelphia is Moderate (median AQI 57): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 36 of December days (2.8%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
December's median AQI of 57 is in line with Philadelphia's whole-year median of 56, so this period is neither a clean nor a dirty stretch for the area. Nationally, the median December AQI across every EPA metro area (95,590 metro-days, 2019–2025) is 39, so Philadelphia runs above the national December norm; 2.8% of its December days topped AQI 100 versus 0.7% nationally (above average).
December is part of Philadelphia's winter season (December, January, February); the winter page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Philadelphia
The latest EPA AirNow observation puts Philadelphia's AQI at 44 (O3). The figures above are multi-year month statistics, not today's reading.
View current Philadelphia air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Philadelphia-Camden-Wilmington, PA-NJ-DE-MD), 2019–2025. Daily AQI per CBSA is the highest AQI reported by any monitor in the area that day; the defining parameter is the pollutant that set it. Month and season statistics pool every such day in the period across all years listed. Retrieved 2026-09-09.